1. Field of the Invention
The present invention relates to an optical transmitter-receiver for single-core two-way optical communication and an optically sending/receiving method.
2. Description of the Related Art
The need for a system for transmitting a signal by optical communication more and more has increased as information communication is varied. If a signal is transmitted by optical communication, a single-core two-way telecommunication line system using one optical fiber and a two-core two-way telecommunication line system using two optical fibers are normally used.
For the single-core two-way optical communication system, an optical transmitter-receiver shown in FIG. 1 is used.
The conventional type optical transmitter-receiver shown in FIG. 1 is required to split an optical path for sending and an optical path for receiving so as to realize single-core two-way optical communication. The optical path for sending means an optical path in which beams outgoing from a laser beam generating source 1002 are reflected by the reflecting surface 1004a of a beam splitter 1004 and are incident upon the end 1011a of an optical fiber 1011 through a focusing lens 1003.
The optical path for receiving means an optical path in which outgoing beams from the optical fiber 1011 are focused with the focusing lens 1003 and are incident on a photodiode 1005 through the reflecting surface 1004a of the beam splitter 1004. That is, the beam splitter 1004 is used for splitting the optical path for sending and the optical path for receiving.
As described above, in sending, beams from the laser beam generating source 1002 are reflected by the reflecting surface 1004a of the beam splitter 1004. However, in case beams are reflected, beams equivalent to some percent of the above beams are directly incident upon the beam splitter 1004 through the reflecting surface 1004a as stray light 1008a. Stray light 1008a incident upon the beam splitter 1004 as described above is also incident upon the photodiode 1005. That is, the photodiode 1005 receives not only light for receiving normally outgoing from the optical fiber 1011 but stray light 1008a as crosstalk. When stray light 1008a is incident upon the photodiode 1005, the signal-to-noise ratio (S/N) of the photodiode 1005 is deteriorated and the transmission distance of the optical fiber 1011 is reduced.
There is also an example of another conventional type that a polarizing beam splitter in accordance with the oscillation and the polarization of the laser beam generating source 1002 is used in place of the beam splitter 1004, however, as a laser beam is also not complete linear polarized light in this case, stray light 1008a cannot be completely prevented from being generated in sending.
As outgoing beams from the optical fiber 1011 are also reflected by the reflecting surface (the mirror finished surface) 1004a of the beam splitter 1004 when the photodiode 1005 receives the above outgoing beams, beams equivalent to some percent of beams for receiving do not reach the photodiode 1005 and are wasted. Received beams reflected by the reflecting surface 1004a of the beam splitter 1004 are incident upon the laser beam generating source 1002 and may instabilize characteristics for oscillating the laser beam generating source 1002.
The present invention is made to solve the above problems and the object is to provide an optical transmitter-receiver and an optically sending/receiving method wherein crosstalk can be prevented from being generated in the case of optical sending/receiving using a single-core two-way optical communication interface circuit and optically sending/receiving efficiency can be enhanced.
The above object of the present invention is achieved by an optical transmitter-receiver based upon an optical transmitter-receiver connected to an optical fiber used for a single-core two-way optical communication channel for sending a first optical signal to be sent to the end of the optical fiber and for receiving a second optical signal sent via the optical fiber and characterized by being provided with beams generating means for emitting a first optical signal, light receiving means for receiving a second optical signal outgoing from the end of the optical fiber and an optical system for making a first optical signal from the beams generating means incident upon the incident end of the optical fiber in a direction different from a direction in which a second optical signal is outgoing from the end of the optical fiber.
The present invention relates to the optical transmitter-receiver connected to an optical fiber used for a single-core two-way optical communication channel for making a first optical signal to be sent incident upon the end of the optical fiber and receiving a second optical signal sent via the optical fiber. The beams generating means of the optical transmitter-receiver emits a first optical signal. The light receiving means receives a second optical signal outgoing from the end of the optical fiber. The optical system makes a first optical signal from the beams generating means incident upon the incident end of the optical fiber in a direction different from a direction in which a second optical signal is outgoing from the end of the optical fiber.
Hereby, as the optical system makes a first optical signal from the beams generating means incident upon the end of the optical fiber in a direction different from a direction in which a second optical signal is outgoing from the end of the optical fiber, the optical path of a first optical signal and the optical path of a second optical signal can be approximately completely made independent. Hereby, as a part of a first optical signal is never received together with a second optical signal by the light receiving means, optical crosstalk (stray light) can be removed from the light receiving means.
In the present invention, after a focusing member focuses a first optical means from the beams generating means, a direction converting element converts the optical path of the focused first optical signal to a direction different from a direction in which a second optical signal is outgoing from the end of the optical fiber and can make the first signal incident upon the end of the optical fiber desirably by providing the focusing member and the direction converting element to the optical system. Hereby, the first optical signal from the beams generating means can be made efficiently incident upon the end of he optical fiber.
In the present invention, desirably if the direction converting element of the optical system is provided with a reflecting film with simple structure for converting the optical path of a first optical signal to a direction different from a direction in which a second optical signal is outgoing from the end of the optical fiber, a first optical signal can be made securely and efficiently incident upon the end of the optical fiber.
In the present invention, desirably if the reflecting film is a total reflection film, a first optical signal can be made incident upon the end of the optical fiber without the loss of the luminous energy of the first optical signal.
In the present invention, if a package for housing the beams generating means, the optical system and the light receiving means is provided and is attached to the end of the optical fiber with the end of the optical fiber directed to the light receiving means so that the package can be detached, the optical fiber can be readily attached/detached to/from the optical transmitter-receiver.
In the present invention, desirably if light shielding means is arranged in the package to prevent beams from the beams generating means from leaking out of the package, beams from the beams generating means can be prevented from leaking out of the package even if the optical fiber comes off the package.
In the present invention, desirably if the light receiving means is arranged outside an area which reflected light generated because a first optical signal is reflected by the end of the optical fiber reaches when the first optical signal is incident upon the end of the optical fiber, crosstalk (stray light) can be more securely prevented from being generated.
In the present invention, desirably if a focusing element is provided to focus a second optical signal and make it incident upon the light receiving means, efficiency for making a second optical signal incident upon the light receiving means can be enhanced.
The above object of the present invention is achieved by an optically sending/receiving method based upon an optically sending/receiving method for making a first optical signal to be sent incident upon the end of the optical fiber and receiving a second optical signal sent via the optical fiber and characterized in that a first optical signal from the beams generating means is made incident upon the end of the optical fiber in a direction different from a direction in which a second optical signal is outgoing from the end of the optical fiber and in addition, the light receiving means receives a second optical signal outgoing from the end of the optical fiber.
Hereby, as a first optical signal from the beams generating means is incident upon the end of the optical fiber in a direction different from a direction in which a second optical signal is outgoing from the end of the optical fiber, the optical path of a first optical signal and the optical path of a second optical signal can be approximately completely made independent. As a result, as a part of a first optical signal is never received together with a second optical signal by the light receiving means, optical crosstalk (stray light) can be removed from the light receiving means.